The way they work is pretty simple: The motor kicks in with extra assist when you pedal, and there are different levels of assistance. That's it. Just turn it on, pedal, and go! You can also turn the assist mode off and ride it like a regular bike. And e-bikes stop assisting at a certain speed (in the U.S., it's 20 mph or 28 mph depending on class) for safety, of course.
“Built to be portable and highly customizable, the Stark Drive Mini e-bike will provide you with everything that you desire for your commute and everyday use. The Stark Drive Mini can easily be folded after you’ve arrived at your destination and conveniently carried into the office or classroom. The Stark Drive is also compact enough to be taken on a plane (adhering to FAA & TSA guidelines), giving you increased mobility wherever your travels take you.”
Electric trikes have also been produced that conform to the e-bike legislation. These have the benefit of additional low speed stability and are often favored by people with disabilities. Cargo carrying tricycles are also gaining acceptance, with a small but growing number of couriers using them for package deliveries in city centres. Latest designs of these trikes resemble a cross-between a pedal cycle and a small van.
E-bikes mostly use motors and battery options from a few major suppliers: Bosch, Yamaha, Shimano, and Brose. A few other brands exist, but are less reliable or powerful. Some, like the Yamaha system, have more torque and others are quieter. But generally all four make good options. Look for motor output (in watts) which will give you an idea of total power. But watt hours (Wh) is perhaps a better figure to use—it takes into account battery output and life to give a truer reflection of power.